As the demand for digital broadcasting-related technology increases, a digital light processing (DLP) technology capable of realizing high resolution is in the limelight. Particularly, the digital micromirror device (DMD) is used for digital light processing systems and serves as a kind of a light switch display device for switching a reflection angle of light to two modes by changing the position of a micromirror in a range of +10 to (−10)°. Intensity of light is controlled using a time for which light is transmitted at a predetermined angle.
A DMD has several hundred thousand to several million micromirror arrays corresponding to pixels for an image to be displayed formed using a semiconductor process. An angle of a mirror is controlled using a voltage applied to each mirror, thereby controlling image data of each pixel.
FIG. 1 is a schematic view of a sub-pixel of a digital micromirror device according to a related art, and FIG. 2 is a photo of a sub-pixel of a digital micromirror device according to the related art.
Referring to FIGS. 1 and 2, the sub-pixel of the digital micromirror device includes a complementary metal oxide semiconductor (CMOS) address circuit board substrate 10, an insulating layer 30, a bias/reset electrode 40, a yoke address electrode 80, first spacers 42, hinge supporters 50, a hinge 60, a yoke 70, a mirror supporter post 22, a mirror 20, second spacers 82, and a mirror address electrode 90.
The hinge supporters 50 are formed in a triangular shape on the first spacer 42 to face the bias/reset electrode 40. The hinge 60 is rotatably connected between hinge supporters 50 formed in a diagonal direction. The yoke 70 is formed in an “H” shape on the hinge 60 and inclined in a range of +10- to (−10)° depending on an address voltage applied to the yoke address electrode 80. A yoke landing tip 72 serving as a spring is formed on each corner of the yoke 70.
The mirror supporter post 22 is formed at a center of the yoke 70 to support the mirror 20, and simultaneously, allow the yoke 70 to be separated a predetermined distance from the mirror 20.
The second spacers 82 are formed a predetermined distance apart in a diagonal direction from each other on the yoke address electrode 80 to support the mirror address electrode 90, and simultaneously, allow the yoke address electrode 80 to be separated a predetermined distance from the mirror address electrode 90.
The mirror address electrode 90 is formed on the second spacer 82 to face the yoke address electrode 80. The mirror address electrode 90 is electrically connected to the yoke address electrode 80 through a via hole formed in the second spacer 82.
The mirror 20 is formed on the mirror supporter post 22 to reflect light incident thereto.
FIG. 3 is a photo image of an off state of a digital micromirror according to a related art, viewed from a front side.
Referring to FIG. 3, a photo image at the left side shows a good state, and a photo image at the right side shows a bad state. In FIG. 3, rhombuses of white spots are spread over all directions. The rhombus means one pixel. The white spots appearing as vertexes of the rhombus, the four sides, and the central point of each rhombus represent light that is incident from a light source reflected by the mirror 20. The white spots appearing as vertexes and four sides of the rhombus represent light reflected to a gap between mirrors 20 of adjacent pixels. Here, the light is due to a metal line formed on a rear side of the mirror 20. The white spot appearing as the central point represents reflected light from the mirror 20 itself. Particularly, examination of FIG. 3 shows that a reflected light amount from the vertexes and the four sides of the rhombus in the photo image at the right side is greater than the reflected light amount in the photo image at the left side.
FIG. 4 is a front photo image by a microscope, illustrating a related art digital micromirror device after an arc hole is formed.
In FIG. 4, the image on the left is similar to the image on the right in FIG. 3. The image on the right is a microscope image of the region shown as a box in the image on the left. Referring to the image on the right, the blue color is a third metal line, and the yellow color is a first metal line and a second metal line formed below the third metal line.
Referring to FIG. 4, the white spots of FIG. 3 at the vertexes and sides of the rhombus coincide with a yellow region.
FIG. 5 is a view illustrating a layout of the sub-pixel illustrated in FIG. 2.
Referring to FIG. 5, a white spot region includes the first and second metal lines, which are visible at the gaps. Light reflected by the first and second metal lines is reflected through a gap A between adjacent mirrors 20 in an off-state.
Therefore, a primary vector reducing a contrast of an off-state is the light reflected by the first and second metal lines.
Consequently, the related art digital micromirror device 20 has a problem that a contrast is reduced by light reflected through a gap between mirrors 20 of adjacent pixels due to metal lines formed on a rear side of the mirrors 20.